Tectonics Of Indonesia

Tectonics of Indonesia

The skype session with my supervisor make me think about what I am gonna do for my PhD journey. I am just about to start my 4-year prae doc program at the University of Vienna. I most likely will doing something with Ambient Seismic Tomography. One thing that quite tempting is to understand Indonesian Tectonics using this promising method.

Indonesia is located between two continental plates: the Eurasian Plate (Sunda Plate) and Australian Plate (Sahul Shelf); and between two oceanic plates: the Philippine Sea Plate and Pacific Plate. Several major and minor plates play important rules to determined the tectonic setting of the Indonesia archipelago.

from Widiyantoro and van der Hilst (1997):
“The junction of island arcs includes the Sunda arc, the Banda arc, the Sangihe arc to the west of the Molucca collision zone (MCZ) and the Halrnahera arc to the east. The Sunda arc, from northwestern Sumatra to Flores, marks the subduction of the IndoAustralian plate beneath the Eurasian plate. The Banda arc to the east of the Sunda arc displays a strong curve in map view.”
“The strike of the Banda arc used to be east-west, just like the eastern part of the Sunda arc, but it was twisted counter-clockwise in the Pliocene due to the combination of the collision with the northward-moving Australian continent, the counter-clockwise rotation of New Guinea, and the westward thrust along the Sorong fault system.”

Mantle Structure Beneath Indonesia

Mantle Structure Beneath Indonesia has been studied by Widiyantoro and van der Hilst (1997) by applying tomographic inversions of traveltime residuals of direct P and the surface-reflected depth phases pP and pwP. The previous studies (did not use depth phases such as pP and pwP) revealed that there are some slabs penetrate beneath e.g. the eastern Sunda arc, Java, and Molusca Sea Plate. The more relatively detail images are obtained likely due to the combination of the use of better data, the use of the ak135 reference velocity model, the inclusion of a global inversion in the regional study, the use of depth phases and the use of gradient damping.

Some features on this study:
“In the top of the lower mantle beneath the eastern part of the Sunda arc, the subducted slab forms a kink, which gradually disappears further west. Beneath Sumatra the image suggests that the slab is detached in the transition zone. The interpreted ‘necking’ of the slab beneath Java coincides with the pronounced existing seismic gap.”
“Further east, beneath the curved Banda arc, the twisting of the slab in the upper mantle is well imaged. The vertical section across the arc, along with the anomaly maps, show that the subducted slab is deflected in the transition zone. A counter-clockwise rotation of the arc has resulted in a spoonshaped structure of the slab complex beneath the Banda Sea. This rotation is probably related to the Pliocene continent-arc collision between Australia and Banda.”

References:

• Widiyantoro and van der Hilst (1997), Mantle structure beneath Indonesia inferred from high-resolution tomographic imaging, Geophys. J. Int. (1997) 130, 167-182

More

• Advances in Geophysics: Seismological Structure of Slabs, page 108, “The Indonesian region is one of the more tectonically complex convergent zones, and slab tomography is useful for studying the distorted slab structures. Puspito et al. (1993) developed a P-wave tomography model beneath Indoensia, based on inversion of 118,203 ISC P-wave times for local and teleseismic events.”
• Tectonics of the Indonesian Region, Warren Hamilton, 1979, free on Google Books

The experts:

• Robert Hall
• van der Hilst
• N.T. Puspito
• Sri Widiyantoro

Future studies:

• New and updated mantle structure images using new data (instruments). Treatise on Geophysics: Seismology and Structure of the Earth (2009) referred to the 1997 model.
• The used of Ambient Seismic Noise mostly apply for upper crustal images -> Whole (Lower) Crust and the Transition Zone.